The present invention relates to a method of testing the mechanical stress resistance of a sample of material in which the movement of two jaws is coupled via the sample and one jaw, as the loading jaw, acts back on the sample with a force which varies with the position of the jaw. It relates furthermore to an apparatus for carrying out this method, the loading jaw being coupled with a force-producing member. It also relates to the use of the method.
Such methods are used, as is known, for testing samples of material, for instance, the compressive strength of tablets, but also, of other samples such as electronic components. Thus it is known, for instance, from Swiss Pat. No. 523 499 of the same applicant, to place such samples of material, and particularly tablets, between two jaws, one of which is driven forward until it contacts the tablet. The two jaws are then coupled in movement via the tablet. The second jaw is also now pushed along, thereby pushing a gravity pendulum out of its vertical position of rest. The pendulum thus acts on the tablet with a force which varies with the position of the jaw. By means of a suitably graduated maximum deflection indicator it is recorded when and upon what deflection of the pendulum the sample of material, and in this case in particular the tablet, breaks.
Other methods are also known in which the position-dependent force is produced by spring arrangements. Each of these methods has the disadvantage that to obtain an unequivocal association between the position of the jaw acted on by the force and the force thereby exerted on the specimen is expensive and/or inaccurate. Furthermore, the problem arises in the known methods that they do not operate with optimal time control in the sense that the movements of the jaws, whether in the forward cycle, and in particular until contact is made with the sample of material, i.e. up to the coupling in motion of the two jaws via the sample of material, and/or in the jaw return cycle, are not so controlled that the measurements are effected as rapidly as possible but without inaccuracies, which, however, time optimalizing in the forward cycle as well as in the return cycle would produce. In this connection, however, it must be borne in mind that the forwardly driven jaw must make such soft contact with the sample of material that the contact momentum will not by itself, particularly in the case of samples of brittle material, lead to breakage phenomena which might not be visible but which would falsify the result.